The purpose of this study is to evaluate the effect, pharmacokinetics and dose proportionality of buprenorphine when administered to non-dependent opiate users. 1) To evaluate whether plasma concentrations of buprenorphine increase proportionally to buprenorphine dose. 2) To evaluate the dose-response of subjective and physiological effects of buprenorphine; and 3) To determine the safety of buprenorphine.